1. Field of the Invention
The present invention relates generally to decapsulation of plastic packaged integrated circuit devices, and pertains particularly to systems and methods for application of etchant materials for decapsulation.
2. Discussion of the State of the Art
Integrated circuits (ICs) function as discrete units and a populated printed circuit board (PCB) final assembly consists of many different types of ICs placed in close proximity. Such devices are often sourced and manufactured elsewhere and are packaged into individual segments with all of the delicate IC components protected within the individual packaging. Plastic encapsulation has been employed for years, typically utilizing epoxy or other plastic resin materials, which involves molding the protective material around the IC device itself, a central portion of lead frame, bonding wires or other connections between the contact pads on the device and the inner lead fingers on the lead frame.
It is clearly desirable that IC failure analysis be performed utilizing non-destructive testing procedures which leave the entire encapsulated package structure intact. However, visual inspection, testing, failure analysis and repair of such encapsulated devices most often require physical access to the packaged components and to the wire bonds, inner lead fingers and other connection circuitry thereof. In such cases decapsulation of the package, at least in part, is necessary to allow for exposure of the circuits of interest from their outer covering, which is a required first step of failure analysis.
Since the advent of IC plastic packaging, several techniques have been developed for removal of the protective material. One such technique, which is mechanical, is to grind the encapsulant back to a point to where the IC and connections are exposed, or the encapsulant may be cut along the sides. Another technique is plasma etching which involves precise application and causing the ionized particles of the plasma to react with the encapsulant material at high temperature, and then draining away the products of the etching process.
The above methods do have disadvantages however. For example, when using the mechanical grinding approach it is difficult to know precisely when to stop the grinding, and physical damage to connections within the package is highly possible. Plasma etching, while being very precise, is in many cases prohibitively expensive, and the fine control required can be cause for a prohibitively lengthy process as well.
Chemical processes that can remove the encapsulant material are generally preferred in the art. Chemical etching provides a balance of precision and cost effectiveness, and involves precise application of an acidic, heated corrosive substance, for example nitric acid and/or fuming sulfuric acid. The process may involve manual or automated jet application of the acid material. Jet etching is a delicate process which requires very careful application of the corrosive material. However, although precise and cost effective, the process does also have certain disadvantages as practiced in current state-of-the-art systems.
Various deficiencies have been encountered in many prior art systems for decapsulating packaged electronic devices. For example, decapsulation systems and methods have difficulty in controlling the desired amount of etching, prevention of damage to the package including interior copper or other metal wires and device metallization, and also the volume of acids required to perform the process. Further, although the use of nitric acid and sulfuric acids or mixtures of the two has been quite successfully used for decapsulating packaged ICs using aluminum metallization and gold or aluminum interconnects, this is not the case for decapsulating devices using the more recent copper metallization for interconnects. Nitric acid is effective at removing the mold compound of the encapsulant, but also removes the upper layer of copper die metallization and will damage the copper interconnect wires. In this case the top interconnect metallization layer is made unavailable for failure analysis. For example, one important test is the wire-to-pad bond test, well-known in the art as the wire pull and ball shear test. This test is performed at the upper metallization layer, and is impossible in the case of such copper metallization damage as a result of prior art etching systems and methods. Sulfuric acid presents the same difficulties.
Further problems exist in prior art systems for decapsulating packaged electronic devices by etching, in that external auxiliary heaters are typically used for heating of the etchant, which can cause a lack of precise maintenance of a select temperature of the etchant mix, etch head, and encapsulated electronic device There is also a problem of a lack of keeping etchant acid consumption low due to the absence of efficient etchant recycling processes. A particular slowness of the etching process exists due to the presence of non-reactive materials on the etch face, and there is inefficient removal of etching debris.
Therefore what is clearly needed is a system and method for decapsulating a packaged electronic device which provides for an efficient and economical etching process utilizing new and novel techniques involving precise temperature control at the etch head, reduced etchant usage through partial etchant recycling, minimal damage to devices that have copper metallization, and faster etching process speed.